As excited as he was to coach Khalil Mack in his second stint with Oakland, Gruden believes the right move ultimately was to trade Mack to give the Raiders the draft picks and salary cap room needed to rebuild a depleted roster.

"It wasn't my goal to trade Khalil when we got here," Gruden said Sunday. "One of the reasons I'm here is because of him. Unfortunately, we had a standoff with a contract, and we could not come to terms. The Bears made us an offer of two first-round draft choices and here we are today."

The Raiders made the blockbuster trade on Saturday, dealing one of the game's most dominant defensive players to Chicago for first-round draft picks in 2019 and 2020, a sixth-rounder next year and a third-rounder in 2020. Oakland also included its second-round selection in 2020 and a conditional fifth-rounder that year in the trade.

Mack then immediately signed a six-year, $141 million extension with the Bears that guarantees $90 million. That's the richest deal ever for a defensive player and nowhere near where the Raiders were willing to go after already committing $25 million a year to quarterback Derek Carr.

"It's tough when you have two players that are the highest paid at their positions, so the economic part of it certainly weighs in," Gruden said. "We've got free agents on our team that are going to be (up) next year; we've got to find a way to bring them back. So you've got to field a 53-man roster and there are some implications of having two players making that much money. That's no mystery to anybody."

The Bears were willing to commit that money in part because they have quarterback Mitchell Trubisky on a rookie deal. The Los Angeles Rams gave $87 million guaranteed to Aaron Donald this past week in what was the richest defensive contract for one day until Mack surpassed it, but they also have quarterback Jared Goff on a rookie contract.

The Raiders don't have that luxury and have several holes to fill on a team that went 6-10 last year and has gotten little production from recent draft classes. Oakland has already cut ties with its second-round picks from 2015, '16 and '17 in Mario Edwards Jr., Jihad Ward and Obi Melifonwu and has only 11 of the 50 draft choices that general manager Reggie McKenzie made from 2012-17 on the 53-man roster.

That has contributed to the Raiders having the oldest roster in the league and the desire for more draft picks.

"We're trying to hit on the draft," Gruden said. "We're trying to draft and develop. Obviously the last three draft classes we haven't got a lot of production out of yet. I don't think there's anybody left from the '13 draft. The '15, '16, '17 (classes), not much production at all. With that being said, you have to fill holes."

Gruden didn't want to second-guess the approach the Raiders took with Mack after exercising the fifth-year option on his rookie deal worth $13.8 million.

The two sides traded offers before the start of the league year in March that were far apart and the Raiders made no more offers after that as Mack held out. Despite the wide gap, the Raiders did not look to trade Mack before the draft when they could have gotten help for this season.

When Donald got his big deal Friday, Oakland saw where the bar was set and made the deal rather than wait to see if Mack would eventually report.

"We would like to have the player stay here; he was under contract," Gruden said. "We did not expect this to last as long as it did. But we're going to be second-guessed until the cows come home on this. I understand that. But, bottom line is, we did do our due diligence, there was a standoff, and he got a great contract from the Bears — a great contract."

Now the Raiders must move on with the season opener coming Sept. 10 against the Rams. There is a big hole on defense as the Raiders try to replace a player who is a two-time All-Pro and the 2016 NFL Defensive Player of the Year. Since entering the league, Mack leads all players with 185½ quarterback pressures and ranks second with 68 tackles for loss, according to SportRadar.

Oakland still has Bruce Irvin as a pass rusher on one side and rookie Arden Key showed promise this summer on the other side. The inside rush should be improved with rookies P.J. Hall and Maurice Hurst, but none of those players are at Mack's level.

Mack also was a leader in the locker room and one of the most popular players, making his loss even bigger. But Gruden felt it was still time to move on, no matter how much he will be missed by his teammates.

"He's a great player and a good teammate and a lot of these guys were very good friends with him," he said. "It was tough but he's been gone for some time. Like I said, we wish him the best. We have to build this football team. We have a lot of needs and we'll address him as we see fit. But it's never easy to say goodbye to anybody, especially a great player."